Process and apparatus for heating hydrocarbon fluids



Dec. 21, 194s.

L. KNIEL 2,456,787

PROCESS AND APPARATUS FOR HEATING HYDROCARBON FLUIDS Filed March 9, 19462 She'ets-Sheet 1 Dec. 2l, 1948. L. KNIEL 2,456,787

PROCESS AND APPARATUS FOR HEATING HYDROCARBON FLUIDS Filed March 9, 19462 Sheets-Sheet 2 TEMPERATURE DEGREES F.

I6 '7 REACTOR COIL- TUBE Patented Dec. 2l, 1948 PROCESS AND APPARATUSFOR HEATING HYDROCARBON FLUIDS Ludwig Kniel, Scandale, N. Y., assignortoThe Lummus Company, New York, N. Y., a corporation oi' DelawareApplication March 9, 1946, Serial No. 653,289

9 Claims. (Cl. 196-110) This invention relates to an apparatus and amethod for heating a hydrocarbon fluid by passage of the fluid throughbanks of tubing within a furnace chamber in which the uid is heatedpredominantly by radiant heat. More particularly, the invention relatesto an apparatus and a method in which the tubes which are subjected tothe greatest heat are protected from overheating by passing through themfluid at a rela.- tively lower temperature than the fluid in other partsof the-same tube bank. This application is directed to improvements overthe disclosure of copending application, Serial Number 594,410, filedMay 18, 1945, by Ludwig Kniel, Pierre Lambert and Herbert R. Treat,forHeating of hydrocarbon fluids.

An important object of this invention is to provide a heating apparatusof high thermal efilciency in the heating of a hydrocarbon fluid, andalso to effect economy in the apparatus.

Another .object of the invention is to provide an apparatus for heatinga hydrocarbon fluid in which the flow of fluid is so arranged as tolimit the maximum temperature which the hottest tubes in the apparatusattain.

Another object of the invention is to provide an apparatus and a methodfor heating a hydrocarbon fluid in which the life of the tubes is at amaximum, and in which coke deposition within the tubes is minimized.

' Further objects will be obvious from a reading of the followingdescription in connection with the accompanying drawings in which:

Figure 1 is a vertical transverse section of a furnace embodying myinvention:

Figure 2 is a partial vertical section on the line 2-2 of Figure 1;

Figure 3 is a graph showing the temperature of the fluid as it passesthrough each of the various tubes vin `my apparatus; and

Figure 4 is a graph showing the rate of heat input-into the fluid as itpasses through the tubes inthe central or` reactor tube bank of myapparatus:

-Myinvention is of particular utility in the thermal cracking of propaneto obtain ethylene as a desired end product, as in the case of thefurnace described in the aforementioned copending application. Infurnaces of this type the `hydrocarbon fluid is passed through banks` oftubes which are heated primarily by radiant heat. The central or reactorbank, or banks, of tubes being subjected on both sides to radiant heat,rather than onone side as in the case of side Wall tubesfhave a muchgreater heat input rate than Astraight countercurrent relation to thecombustion gases, the tubes nearest the burners have been exposed toespecially high temperatures,

which has the undesirable effect of reducing the tube life andnecessitating frequent shut downs for replacement of tubes or fortheirrepair. Such a condition obviously reduces the efficiency of a furnacein requiring its being shut down for such replacement or repairs and inthe cost of tubes. My invention is designed to eliminate this condition,or at least substantially to reduce it so as to give increased tube lifeand to minimize the frequency of required shut downs for repairs.

Referring to the .mbodiment of the invention shown in Figures 1 and 2 ofthe drawing, the furnace chamber I0 is a box-like form having a fiatiioor or hearth II, a flat roof I2, opposite side walls I3, and verticalend walls I4 and I5. The lower portions of the side walls I3 arevertical, and the upper portions I3a converge upwardly to the roof. Thechamber is constructed of blocks or slabs of refractory material sheatedwith heat insulation I6. The furnace is supported in a position elevatedfrom the ground or from a foundation by a metal frame structurecomprising columns Il and upper and lower girders I8 and I 9.

Within the furnaces chamber a pair of outer tube banks, 20 and 2I, aresupported in vertical positions directly inwardly of the verticalportions of the side walls I3, and a central, or intermediate, tube bank22 is supported in a vertical position between said outer banks. bank isarranged parallel to the outer banks. A relatively low wall 23 extendsupwardly from the floor of the furnace chamber. This wall is formed ofrefractory blocks or slabs and internal metal structures 24 spaced alongthe wall. central tube bank extends from the wall 23 substantially tothe roof I2, and together with said wall divides the furnace' chamberinto two comf bustion zones,vA and B. At the bottom of each of saidzones, there arerows of burners 25, the rows extending longitudinallyalong the furnace chamber and the burners being in staggered positionsin the rows and directed upwardly through ports in the floor. Theburners are adustable to vary the heat input in the two zones. The roofof the furnace chamber has two outlets. 23 and 21, opening from thezones A and B into This central TheA exhaust ducts 28 and 29,discharging products of combustion from the furnace chamber. The outlets26 and 21 and the ducts 28 and 29 preferably extend substantially thevlength of the furnace. chamber, and the ducts have dampers 30 and 3| foradjusting the draft through the furnace.

Each of the three tube banks comprises a single nections 34, saidoutlets are joined to the inlet of the central bank at its lower end. Ata few tubes from the bottom of the central bank,

preferably an odd number of such tubes, a crossover or transfer line 36conducts the fluid to the top tube of the central bank, and thereafterthe fluid iiowsjdownwardly through the remainder of the tube bank untilit finally exits from the furnace, as through the dischargeline 31. Allof the banks, including their return bends, are conned within thefurnace chamber and extend throughout most of the length of the chamber.

The tubes of the central bank are subjected to greater heat than thetubes of the outer banks, and they consequently require more frequent'servicing and replacement. Therefore, provision is made for readyrenewal of the central bank. The frame structure which supports thefurnace carries a horizontal track 38 extending over the top of thefurnace. 'I'his track lies in thev vertical plane of the central tubebank and', through a plurality of suspension connections 39, the bank issupported by the track. The suspension connections extend through slots40 in the roof I2.

Hinged closures 4| close the portions of the slot between the suspensionconnections 39 and also close the portions adjacent the ends of thefurnace chamber. These closures are formed on their inner sides ofrefractory material. The end wall |'4 of the furnace chamber has avertically elongated aperture or slot 42 in register with the adjacentside edge of the bank 22 and meeting the slot 40 through the roof. Theslot 42 is normally closed by a hinged closure or door 43 formed at itsinner side of refractory material. After de taching the pipe connections34 and 31 and open ing the top doors 4| and side door 43, the tube bank22 may be pulled along its track outwardly through the slot 42 to theexterior of the furnace chamber where it may be conveniently serviced. f

In Figure 3, I have shown the temperaturev of the ,fluid as it passesthrough the various tube coils in the furnace. In the graph, the sidewall tube banks have been assumed to have eight tubes each, and thecentral or reactor tube bank and that any other paths oi' ow of thefluid through the side wall banks may be employed, such, for example, ashaving the fluid enter the bottoms of said tube banksand flow upwardlythrough them. Within the banks the charge is qiuckly preheatedpredominantly by radiant heat, including that received directly fromcombustion within the zones A andBtalndfthat received throughre-radiation from the wall l23. While the tubes of these banks areheated predominant-- ly -upon one side, there is no danger of cokedeposition, since the charge is cool when it enters the banks and doesnot remain therein long enough to reach a coking temperature. Theprovision oi these banks avoids the requirement for the' customarybonvection heating bank and the chambercontaining such a bank andeffects more eilicient and quick preheating than can be attained byconvection heating.

The preheated charge is passed from the lower ends of the banks 20 and2| through the connections 33, 34, and 35 to the lowr end of the centraltube bank 22. This central tube bank is subjected to radiant heatdirectly from the products of combustion in zones A and B and also toheat reradiated from the walls I3, including their upper, slopingportions |3a. This bank.. particularly in its upper tubes, may also be'subjected to heat of convection as one of the dampers 30 and 3| isnormally closed and the other one open, so that the products ofcombustion in both zones A and B exit through the same outlet 26 or 21.'Thus, the products of combustion in one zone,A

21 and there would be'substantially no ow ofgases through the tubes incentral bank .22.

' In the bank 22, the charge passes progressively upward, preferablythrough an odd number of tubesv to the crossover connection 36 throughwhich it passesto the upper tube of the bank 22, and then vpassesprogressively downward through the remainder of bank 22 todischargeconnection' 31. The number of tubes vincludedbetween theconnection 35 and 36 in the lower, and i'lrst,

. section of bank 22 is preferably an odd number for the reason that theinlet 35 and the outlet 31 of said bank 22 preferably pass through thesame end wall I5 of the furnace, as indicted in Figure 2. 'I'here beingno connection of the central tube bank-l 22 to the other end wall I4 ofthe furnace, provision is thereby made for expansion and contraction ofthe tubes with changes in temperature. By virtue of passing ,thepreheated uid first through the lower tubes of'the intermediate bank 22while the uid is still at a relatively low temperature, the lower tubes,which are subjected to the greatest degree of heat, are prevented fromhas been shown ashav'lng fourteen tbes, the

lower three of which are the rst ones into whic uid from the side walltubes flows.

In Figure 4, I have used the same tube numbering in showing the rate oiheat input, but only for the tubes in the central' or reactor tube bank.

In the operation of this furnace, the' charge to be heated iscontinuously introduced into the upper ends of the outer tube banks 20and 2| and passed progressively downward therethrough in parallel. It isto be understood that this arrangement is not an essential part of myinvention,

A tion of heat is graphically illustrated in Figure 4,

where it will be seen that the rate of absorption' of *heat in the lowerand first tubes numbered 3,

Il and Il, in central bank 22. is much greater than that in the othertubes of the reactor coil. numbered l2 through 22.

This arrangement of fluid flow makes possible an unusually enlcient andreliable-furnace requiring a minimum of upkeep. As described in thepreviously mentioned copending application, the provision of side walltube banks 2l and 2l permits rapid preheatlng of the charge. but at thesame time does not permit coking in the side wall tubes, as the fluiddoes not attain a sufficiently high temperature for coke to form.

"The exit temperature from the side wall tube bank is kept belowapproximately 1000 F. Due to the fact that they are kept relativelycool,the side wall tubes can be made of low carbon steel and hence are ofcomparatively low cost. The tubes in the center row are made of allowsteel to withstand the higher temperatures to which they are subjected.

Coking is also minimized in other parts of the furnace, because thetubes are sovdisposed that there are few, if any, relatively cold spotswhere coke deposition wiuld be likely to occur. Coking or carbondeposition is inhibited by the tubes in which the fluid fis at a highenough temperature for carbon deposition, that is. those in the centralor reactor coil, being heated substantially uniformly about theirperipheries.

The exit from the lower part of the center 'row of tubes through thetransfer tube is arranged to take place at `a temperature just beforecoking tends to occur. Up to this temperature, the amountof ,coke `whichmay form is sufficiently low so that the velocity of vapors through thetransfer tube will effectively carry all of it to the top of the tubes,after which it will pass through the tubes aided by graviy and,therefore, 'without tending to clog the tubes.

Another advantage of my invention isthat feeding of the preheated uidfirst into the hottest tubes of the reactor coil accomplishesa rapidrise in the temperature of the fluid to a cracking temperature. This canbe seen from an inspection of Figure 3, in which the steepest rise ofthe temperature curve is at tubes 9, Ill and il, and of Figure 4, whichshows that in those tubes the rate of heat absorption is greatest. Thisrapid rise of temperature is important because it suppresses carbondeposition, which occurs more readily when the temperature rise isslower.

Finally, in the furnace of my invention, I overcome a disadvantage foundto occur in prior constructions of this general type, namely, thetendency of tubes which are subjected to the greatest heat to failfrequently and to require replacement or repair.'

It is to be understood that the embodiment shown in the accompanyingdrawings and described above is merelyillustrative, and that myinvention may take other specific forms, such, for example, as a furnacehaving three combustion Ychambers and two intermediate tube walls, asshown in the above-mentioned copending appli` cation. Forms andembodiments otherthan those shown in this and the previous application,are likewise within the scope of my invention, and are to be consideredas included by it where they are within the scope of the appendedclaims.

Having thus clearly described my invention, what I claim as new anddesire to secure by Letters Pattent is:

l. The method of heating a hydrocarbon fluid, comprising conductingcombustion within two side-by-side zones to eil'ect a high degree ofheating within regions of one end of, the zones and progressivelydiminishing heating toward the opposite end of the zones. conductingsaidfluid in separate streams along confined courses within said highlyheated regions and at the remote sides thereof and, within said courses,effecting preheating of the fluid predominantly by radiant heat, unitingsaid -streams of the fluid thus preheated and conducting the pre--heated fluid along a relatively short confined course'between saidhighly heated regions and in substantially. equal exposure to radiantheat from said regions simultaneously andfrom the two regions,v togetheraround substantially the entire cross section of the course, conductingthe fluid from said relatively shortcourse to a point between regions ofthe opposite-end ofthe zones and-thence along a longer confined coursebetween the zones and in substantially equal exposure to radiant heatfrom said zones simultaneously and from l the vtwo zones together aroundsubstantially the entire cross section of the course, and, in saidlonger course, advancl ing the uid progressively toward said highly;v

heated regions, and conducting combustion gases of at least one of saidzones over said longer course t-o heat the fluid therein by con-lvection also.

2. The method of heating a hydrocarbon fluid, comprising conductingrcombustion within two sideby-side zones to effect a high degree heatingwithin regions at one end of the zones and progressively diminishingheating toward the opposite end of thezones, conducting said fluidiriseparate streams along confined courses within said highly heatedregions and at the 'rfmote` sides thereof and, within said courses,effecting preheating of the fluid predominantly by radiant heat, unitingsaid streams of the fluid thus preheated and conducting the preheatedfluid along a relatively short confined course between said highlyheated regions and in substantially equal exposure to radiant heat fromsaid regions simultaneously and from the two regions together aroundsubstantially the entire cross section of the course, and conducting thefluid from said relatively short course to a point between regions ofthe oppositeA end of the zones and thence along a longer conllned coursebetween the zones and in substantially equal exposure to radiant heatfrom said zones simultaneously and from the two zones together aroundsubstantially the entire cross section of the course, and, in saidlonger course, advancing` comprising conducting; combustion predoml-.

nantly within lower regions of two slde-by-side zones, passing saidfluid in two separately confined streams and in the same generalvertical direction along two substantially coextenslve serpentinecourses at the opposite outer sides of said zones to preheat the fluidpredominantly bv radiant heat, combining said streams after passagethrough said courses, passing the fluid of the combined streams along arelatively short confined course between said lower regions andsubstantially midway between said flrst courses. passing the fluid fromsaid relatively short course to a point a substantial distance above thelatter and thence downwardly along a relatively long serpentine coursebetween said zones and substantially midway between said vfirst courses,

substantially symmetrically with respect to said plane, adjacentopposite side walls of the chamber and defining first courses for theuid, a

- single row of spaced substantially parallel tubes located within saidplane between said outer banks and dividing the chamber into twosubstantially duplicate combustion zones, a minor number of tubes ofsaid row atone end ofthe row beingf serially connected and deiining asecond course forthe iiuid with an inlet and an outlet, and theremaining tubes ofthe row being serially connected and defining a thirdcourse for the fluid with an inlet at the opposite end of the row and anoutlet adjacent said second course, a fluid delivery connectionbetweenleach outer bank and the inlet of said second course,

a fluid delivery connection between the outlet of said'second course andthe inlet of said third course, burnermeans arranged to conductcombustion within regions of said zones adjacent said second course andat oppositesides thereof, and outlet means disposed for passing productsof said combustion from regions adjacent the inlet end of said thirdcourse.

6. A heater for hydrocarbon uid comprising a furnace chamber, a pair ofouter banks of tubes within -said chamber, adjacent opposite side wallsthereof and defining rst courses for the uid, aj single row of spacedsubstantially parallel tubes located within a plane substantial- 1ylmidway between said outer banks and dividing the chamber into .twoside-by-side combustion zones, a minor number of tubes of said row atone end of the row being serially connected and defining a second coursefor the fluid with an inlet and an outlet and the remaining tubes of therow being serially connected and defining a third course for the fluidwith an inlet at the opposite end of the row and an outlet adjacent saidsecond course, a fluid delivery connection between each outer bank andthe inlet of said second course, a uid delivery connection between theoutlet of said second course and the inlet of said third course, burnermeans arranged to conduct combustion within regions of said z'onesadjacent said second course at opposite sides thereof, and outlet meansdisposed for passing products of said combustion from regions of saidzones adjacent the inlet end of said third course.

7. A heater as claimed in claim 6 wherein the portion of said row oftubes defining Vsaid third course extends materially beyond said outerbanks, and the oppositewalls of the chamber' have portions thereofdisposed to reflect radiant heat of said combustion predominantly uponopposite sides of the tubes defining said third course.

8. A heater as claimed in claim 6 wherein thel said burner meanscomprises a plurality of burners within each zone spaced longitudinallyof the tubes of said row and directed toward the regions adjacent theinletend of said third course.

9. A heater for hydrocarbon fluid comprising a combustionchambersubstantially symmetrical with respect to a central plane, asingle row of spaced substantially parallel tubes within said plane anddividing the chamber into a pair of substantially duplicate combustionzones, a minor lnumber of tubes of the row at one end of the row beingserially connected and defining a relatively short course for the fluidwith an'inlet and an outlet, and the remaining tubes of the row beingserially connected and defining a relatively long course for the uidwith an inletv at the opposite end of the row and an outlet adjacentsaid short course, means to deliver the fluid to the inlet of said shortcourse, a uid delivery connection between the outlet of said shortcourse and the inlet of said long course,

Vand burner means arranged for combustion of radiant heating of thetubes of the row, the individual tubes ofthe row being exposedtransversely around substantially their entire circum ference to receiveradiant heat from both zones simultaneously and substantially equally,and outlet means disposed for passing products of said combustion fromregions of said zones adjacent the inlet end of said longer course.

' LUDWIG KNIEL.

REFERENCES CITED The following references are of record in the leof thispatent:

. UNITED STATES PATENTS Number I

